Pressure sensors that use a semiconductor piezoresistance effect are small and light, and have high sensitivity, and thus are used broadly in fields such as industrial instrumentation and medicine. This type of pressure sensor includes a semiconductor substrate that is provided with a diaphragm portion, a glass pedestal wherein is formed a pressure introducing hole, and a metal base (a stem). Additionally, the semiconductor substrate is bonded to the top surface of the glass pedestal using an anode bonding method. Additionally, the metal base is bonded to the bottom surface of the glass pedestal through soldering.
Because solder has poor wettability with glass, normally a metal thin film layer (a metallization layer) is deposited on the bottom surface of the glass pedestal. The metal thin film layer is deposited on the bottom surface of the glass pedestal using a vapor deposition method or a sputtering method. The hole diameter of the pressure introducing hole in the glass pedestal is essentially uniform between the top and bottom surfaces of the glass pedestal, and thus at the time of the deposition of the metal thin film layer, a metal thin film layer is formed also on the side walls of the pressure introducing hole. Because of this, the solder wets also onto the portions of the side walls of the pressure introducing hole whereon the metal thin film layer is formed. In other words, the solder creeps up the side wall of the pressure introducing hole. Moreover, it is difficult to control the range over which the metal thin film layer is deposited onto the side wall of the pressure introducing hole. Because of this, it is difficult to control the height to which the solder creeps up the side wall portion of the pressure introducing hole. Moreover, it is possible for the solder to creep until it nears the semiconductor substrate. Doing so can affect the semiconductor substrate, such as causing stresses (thermal stresses) caused by differences in coefficients of thermal expansion between the solder and the semiconductor substrate. Additionally, these thermal stresses, and the like, may lead to defects in the characteristics of the semiconductor substrate.
Given this, Japanese Unexamined Patent Application Publication H10-030972 (“JP '972”) describes a pressure sensor that uses a glass pedestal wherein a tapered pressure introducing hole has been formed. Specifically, the diameter of the pressure introducing hole gradually becomes larger towards the top surface of the glass pedestal from the bottom surface. This makes it possible to prevent the deposition of the metal thin film layer on the side walls of the pressure introducing hole when depositing the metal thin film layer on the bottom surface of the glass pedestal. This makes it possible to prevent the solder from creeping up the pressure introducing hole.
However, in the pressure sensor as set forth in JP '972, essentially no metal thin film layer is deposited on the side wall of the pressure introducing hole when depositing the metal thin film layer on the bottom surface of the glass pedestal using the sputtering method. Moreover, there is essentially no wetting of the side wall of the pressure introducing hole with solder. Because of this, it is possible that the strength of bonding between the glass pedestal and the metal base will be inadequate.
Furthermore, in the pressure sensor as set forth in JP '972, the excess solder will pool in the pressure introducing hole, so the pressure introducing hole may become blocked with solder.
The present invention is to solve these problems areas, and the object thereof is to provide a pressure sensor and manufacturing method capable of suppressing more effectively the occurrence of characteristic defects and capable of increasing the strength of bonding between the glass pedestal and the metal base.